For our information:

Just learned that those who are eligible for Social Security, but have not yet signed up for it, are entitled to the amount you would have received had you signed up upon eligibility.

Husb in this situation, and even tho he's still working, and may continue so for a while, he's got some health type problems; may hang on for a while. Soc Sec. sending him a pretty big check this week, for the 'arrears.'